Emotions serve essential functions for survival and social communication. Multiple brain areas are recognized as part of the emotional brain, yet how they generate emotions it is currently unknown. The overall objective of this project is to fil this gap in our knowledge and determine how functional interactions between the multiple areas of the emotional brain generate internal states of emotion, what their defining properties are, and how they are expressed in behavior. The approach consists of three components. In Specific Aim 1, activity patterns of the most sophisticated effector of the emotions, the facial expression system, will be monitored with a new recording device, and the statistical properties of these patterns and their transitions will be quantified. The objective of this aim is to objectiely define and automatically detect emotional expressions of the face. In Specific Aim 2, the emotional brain will be harnessed to sensory cues and observable responses using social reflexes, in which seen emotional faces are briefly but reflexively mimicked by their observers. Whole-brain functional magnetic resonance imaging will localize the nodes of the circuit mediating this behavior, and subsequent electrophysiological recordings will identify information flow and transformation through the nodes of this circuit. In Specific Aim 3, the multiple nodes of the emotional brain identified in the literature will be targeted for massively parallel electrophysiological recording to obtain spatiotemporally precise activity profiles from distribute neural circuits during a wide range of behavioral states. These data will be used to infer functional interactions between emotional brain circuits and to determine whether they form discrete or graded activity states, mutually exclusive ones or mixtures, comprising localized or distributed activity. These results will allow for an objective characterization of emotional state and an evaluation of major current theories of the emotions. The outcomes of this project are expected to have major impact on the affective neurosciences, by directly addressing its most fundamental question; motor neuroscience, by revealing the coding principles of the facial expression system; social neuroscience, by deriving the 'vocabulary' of non-verbal communication; and systems neuroscience, by revealing how global distributed activity states interact with local information processing. Disturbances of the emotion and its facial expression are characteristic of many psychiatric disorders including bipolar mood disorders, schizophrenia, or autism spectrum disorders. The project thus meets the strategic objective of the National Institute of Mental Health in pursuing an integrative understanding of a basic brain-behavior process to provide a firm foundation for understanding mental disorders.